The invention relates to a drive device, in which a movable element can be driven by an actuator via a gear unit and in which the gear unit comprises a motor pinion, an intermediate wheel and a toothed ring, and the intermediate wheel comprises a pinion and a gearwheel, the pinion and the gearwheel being connected via a ratchet in such a way that the pinion connected fixedly in terms of rotation to the ratchet can be rotated in relation to the gearwheel in the manner of a locking pawl.
To control the quantity of fresh gas of a motor vehicle, throttle valve assemblies are usually used. Throttle valve assemblies comprise a housing with a throttle orifice and a throttle member arranged in the throttle orifice. The throttle member conventionally comprises a throttle valve which is arranged on a throttle valve shaft and which is arranged pivotably in the housing of the throttle valve assembly. The throttle valve assumes a defined position in the throttle orifice for the passage of a defined quantity of fresh gas. For this purpose, the throttle valve shaft can be activated mechanically or electromechanically.
In an electromechanical activation of the throttle valve shaft, the throttle valve assembly normally has a position detection means, via which the current position of the throttle valve shaft can be detected. Depending on the in each case current position of the throttle assembly, the current position being indicated by a signal, another signal is then generated either inside or outside the throttle valve assembly, by means of which the throttle valve shaft can be activated via the actuator arranged in the throttle valve assembly. In this case, depending on the position of the throttle valve shaft and consequently of the throttle valve, the throttle orifice is partially closed by the throttle valve, this corresponding to an open position of the throttle valve, or else is also closed completely by the throttle valve, this corresponding to a closing position of the throttle valve.
If the actuator adjusts the throttle valve position from open to closed, the actuator current is switched off only after the throttle valve shaft, together with the throttle valve arranged on it, assumes a position in which the throttle valve substantially closes the throttle orifice. However, after the actuator or its current has been switched off, it still rotates a little further on account of the kinetic energy of its rotor. Consequently, the actuator transmits kinetic energy to the gear unit. The gear unit should absorb the kinetic energy without being damaged. If, however, the throttle valve shaft is in a position which corresponds to the closed position of the throttle valve and the throttle valve bears mechanically, in the closing position, against a step in the throttle orifice, the gear unit, on account of the kinetic energy transmitted to it, will attempt to rotate the throttle valve beyond the step in the throttle orifice. Since the abutment is normally harder than the gearwheels of the gear unit, this often results in a fracture of individual gears of the gearwheels of the gear unit, without the throttle valve being pivoted by the throttle valve shaft. This foreseeable gear unit damage considerably shortens the useful life of gear units of this type, as a result of which their use, particularly in throttle valve assemblies, is uneconomical.
Such a drive device is known, for example, from EP 0 272 352 A2. Herein, the intermediate gearwheel has a ratchet. The gearwheel has a ring of detent pawls and the pinion has ratchet geometries prestressed in relation to the detent pawls. The pinion is manufactured in one piece with the ratchet geometries. The ratchet consequently prevents excess kinetic energy from being transmitted to the movable element. One disadvantage of the known drive device, however, is that the gear unit has a high weight. The high weight of the drive device decisively contributes, however, to the generation of the excess kinetic energy.
It is known from US 6,189,507 B1, in a drive device, to design the toothed ring as a part-toothed ring. This leads to a reduction in weight. This drive device has the disadvantage, however, that the remaining kinetic energy is transmitted directly to the movable element, thus resulting in a short useful life of the drive device.